Electric discharge modulating system



Au 11, 1936. I F, B, STONE 2,050,474

ELECTRIC DISCHARGE MODULATING SYSTEM Filed Jan. 31, 1955 IN VENTOH E'ed B. St one H'I'T'O FINEY Patented Aug. 11, 1936 UNITED STATES PATENT OFFICE ELECTRIC DISCHARGE MODULATING SYSTEM Delaware Application January 31,

'7 Claims.

The present invention relates to electric discharge modulating systems and more particularly to a system of that character wherein modulation or signal mixing is effected in a single electric discharge device or tube. A specific system of the character referred to, and to which the invention is particularly adapted, is known commercially as a combined detector-oscillator wherein a single electric discharge device or tube functions in connection with an oscillator circuit and a first detector circuit, as a signal mixing device.

An electric discharge device adapted for use in a combined detector-oscillator circuit may be of the pentagrid converter type such as an RCA6A7 tube, having a cathode, an output anode, a signal input or control grid more adjacent to the anode, an oscillator grid and an oscillator anode electrode more adjacent to the cathode than the signal grid, and a screen grid for the signal grid.

Although screening is employed and suitable shielding of the external circuits, it has been found that the signal grid may have an appreciable mutual conductance to the oscillator anode, resulting in a degree of undesired energy transfer between the detector and oscillator portions of the system depending upon the frequency to which the oscillator is tuned with respect to the signal frequency. The energy transfer by regeneration or degeneration may be sufiicient to appreciably impair the operation at ultrahigh frequencies such as are used in certain signal bands with all-wave receivers.

Accordingly, it is an object of the present invention to provide an improvedmodulating orsignal mixing system embodying a single electric discharge device, wherein degeneration or regeneration in the signal input circuit is prevented more effectively, and whereby such system may be operated at ultra high frequencies with improved efficiency.

It is a further object of the present invention to provide an improved electric discharge device for signal mixing circuits and the like having two anode electrodes, one being more adjacent to the cathode than the other, and a signal input or control electrode between said anode electrodes, wherein the effect of mutual conductance between the signal input or control electrodes and one of the anode electrodes is materially reduced.

The invention will, however, be understood from the following description when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

1935, Serial No. 4,213

In the drawing, Figure 1 is a schematic circuit diagram of a modulation or signal mixing system embodying the invention, and

Fig. 2 is a schematic representation of a modification of an electric discharge device or tube 5 adapted for use in the circuit of Fig. l, in accordance with the invention.

Referring to Fig. 1, 5 is an electric discharge device having a cathode I, an output anode electrode 9 and a control or signal input grid I I. The de- 10 vice is further provided with an additional grid electrode l3 and a second electrode I5 serving as an anode electrode, both being located between the cathode and the control grid. The device is also provided with a screen grid Il-l'| serving to shield the control grid I I from both the anode 9 and the electrodesl3 and I5.

In connection with this device is shown a usual pentagrid converter or combined detector-oscillator circuit, comprising a signal input circuit 2!, a signal output circuit 23 and an oscillator circuit 25, the input circuit being connected with the control grid ll through a lead 21, and the oscillator circuit being connected with the electrodes l3 and I5 and including a feed-back wind- 25 ing 29 in circuit with the electrode l5 and coupled with the circuit 25 for utilizing said electrodes as an oscillator. The oscillator anode I 5, the screen grid [1 and output anode 9 receive suitable operating potentials from tap points 3! on a suitable 30 potential source such as a resistor 33 which is supplied with rectified or direct current through leads -B and +3.

Biasing potential for the oscillator grid [3 is provided by the usual coupling condenser 35 and 35 grid leak 31, while biasing potential for the con-'- trol grid l I is provided through the input circuit 2! and an automatic volume control circuit connection 39 in series therewith, and a self-bias resistor 4! in the cathode lead 43.

In a radio receiving system of which the circuit shown may form a part, high frequency signals are supplied through the circuit 2| from a suitable source such as a high frequency circuit 45, and. are mixed in the electronic stream of the device 5 with oscillations provided by the circuit 25-29 and the electrodes 13 and I5, to provide an intermediate frequency in the output circuit 23. An intermediate frequency output circuit,

coupled with the circuit 23, is indicated at 41, and

may lead to a suitable intermediate frequency amplifier (not shown). As this type of combined detector-oscillator is at present Well known and understood, further description is believed to be unnecessary.

The circuit thus far described may, however, be taken as representing any modulating or signal mixing circuit or system embodying a single electric discharge device having a plurality of electrodes including a signal input electrode and two anode electrodes, one of which is more adjacent to the cathode and with which the control electrode or signal grid has a negative mutual conductance.

It has been found that when the circuits 2 I, 25, and 29 are operated at relatively high frequencies such as are now generally employed in all-Wave receivers, for example, there is a degenerative effect upon the circuit 2| connected to the detector or input grid II. This has been found to be caused in part by the mutual conductance of the control grid I I on the current to the electrode I5 which operates as the oscillator anode. This mutual conductance is negative in the usual sense. That is, making the grid more negative causes the current to the anode electrode I5 to increase. At the same time its mutual conductance to the main anode 9 is normal, or positive, the anode current through the electrode 9 being decreased in value when the grid I is made more negative.

The increase of current to the anode I5 causes an increased potential drop across the inductance 29 and the resulting potential is applied, through the tube capacity between the electrode I5 and the electrode I, to the input circuit 2| substantially out of phase with the incoming signal.

In a combined detector-oscillator or mixer tube which is satisfactory in operation, the interelectrode capacity between the control grid and the oscillator anode electrode, in spite of suitable shielding or screening, is efi'ective at the higher frequencies to permit feed-back coupling of the type described.

The feed-back is degenerative with respect to the signal applied to the control grid when the oscillator circuit is operated at a higher frequency than the incoming signal, which is the usual condition. If the oscillator is operated at a lower frequency than the incoming signal, the feedback is regenerative which may also be undesirable.

In order to prevent undesired degeneration and regeneration effects in the input circuit of a combined detector-oscillator or mixing tube, the tube element geometry is so arranged that while the device may function as a mixer or converter effectively, the mutual conductance of the control grid II to the electrode l5 and to an electrode 5| are numerically as nearly equal as possible. It has been found that the electrode 5| may be inserted in the electronic stream of the device 5 more adjacent to the main anode electrode, whereby the control grid may have a mutual conductance thereto equal and opposite to its mutual conductance to the oscillator anode electrode I5. The capacitances between the control grid I I and the electrodes I5 and 5| are also, preferably, as nearly equal as possible.

With this arrangement, the mutual conductance from the grid II to the electrode 5|, being positive, operates in a direction to cancel the effect of the negative mutual conductance to the electrode I5, when the two electrodes I5 and 5| are connected in circuit with each other as indicated at 53.

In practice the electrodes I5 and 5| are preferably of similar construction and may be in the form of grids, rods or plates located in the electronic stream of the device on opposite sides of the control grid In the present example, they are shown as being grid-like in structure.

In Fig. 2, to which attention is now directed. the device 5 is shown with the electrodes in the form of rods or plates 55 and 56, the rods or plates 55 being located on one side of the control grid I I while the rods or plates 56 are located on the opposite side of said control grid in the electronic stream of the device. Any suitable construction, however, may be employed which permits the passage of electrons from the cathode I through to the anode 9. The rods or plates 55 or 56 represent any suitable number of such elements interconnected to form electrodes having opposing mutual conductance with respect to the control grid II.

While the invention has been described in connection with a mixing device or modulator of the pentagrid converter type, it should be understood that any suitable electric discharge device 9 may be employed which is adapted for signal mixing in connection with a plurality of signal circuits, and which is further adapted for neutralizing the eifect of mutual conductance of control or signal input grid, and an electrode to which 2 it has a negative mutual conductance and in circuit with which there is suificient impedance to cause feed-back coupling to the said signal input grid.

I claim as my invention:

1. In an electric signalling system, the combination of an electric discharge device having a signal input electrode, a signal output electrode and additional oscillator electrodes coupled to generate oscillations including an oscillator anode electrode to which said input electrode has a mutual conductance, and means for providing in connection with said oscillator anode electrode a second electrode to which said signal input electrode has substantially an equal mutual conductance of opposite polarity.

2. In an electric signal receiving system, the combination of a detector-oscillator comprising an electric discharge device having a cathode, an oscillator grid, an oscillator anode electrode, a signal grid and an output anode, and signal input and output circuits and an oscillator circuit connected therewith to provide signal mixing therein, and means including an additional electrode for preventing energy transfer through said device from the oscillator circuit to the signal input circuit, said electrode having a mutual conductance with the signal grid substantially equal and opposite in polarity to the mutual conductance of said signal grid with the oscillator anode electrode, and being connected with the oscillator anode electrode.

3. In an electric signal receiving system, the combination of a detector-oscillator comprising an electric discharge device having a cathode, an oscillator grid, an oscillator anode electrode, a signal grid and an output anode, and signal input and output circuits and an oscillator circuit connected therewith to provide signal mixing therein, and an electrode having a mutual conductance with the signal grid substantially equal and opposite in polarity to the mutual conductance of said signal grid with the oscillator anode elec trode, and a connection between the oscillator anode electrode and said additional electrode, thereby to neutralize the last named mutual conductance.

4. A combined detector-oscillator comprising an electric discharge device having a cathode, an output anode and a plurality of electrodes interposed therebetween along the electronic path and comprising a control grid adjacent to the cathode, a second control grid more adjacent to the anode, a screen grid for said last named electrode, a second anode electrode more adjacent to the first named control grid and the cathode, an impedance device in circuit with said second anode electrode, means for supplying feed-back energy from said last named electrode to said first named control grid, and means for neutralizing the mutual conductance between the second named control grid and said second anode electrode.

5. A combined detector-oscillator comprising an electric discharge device having a cathode, an output anode and a plurality of electrodes interposed therebetween along the electronic path and comprising a control grid adjacent to the cathode, a second control grid more adjacent to the anode, a screen grid for said last named electrode, a second anode electrode more adjacent to the first named control grid and the cathode, an impedance device in circuit with said second anode electrode, means for supplying feed-back energy from said last named electrode to said first named control grid, and means for neutralizing the mutual conductance between the second named control grid and said second anode electrode, said last named means including an additional electrode corresponding to said second anode electrode located more adjacent to the main anode electrode, and means providing a circuit connection between said additional electrode and the second anode electrode.

6. In an electric signal modulating system, the combination of an electric discharge device having a control grid and an oscillator anode electrode to which the control grid has a mutual conductance, and means providing a second electrode to which the control grid has an equal mutual conductance of opposite polarity, said second electrode being connected with the first named oscillator electrode, thereby to neutralize the first named mutual conductance.

7. In an electric signal modulating system, the combination with signal input and output circuits, of an electric discharge device having a cathode, a signal output anode, a signal input grid and an oscillator anode electrode to which the control grid has a mutual conductance, and means providing a second electrode to which the control grid has an equal mutual conductance of opposite polarity, said second electrode being connected in circuit with said oscillator anode electrode, thereby to neutralize the said mutual conductance.

FRED B. STONE. 

